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ADM1023 Datasheet PDF : 12 Pages
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ADM1023
Table VI. Configuration Register Bit Assignments
Bit Name
Function
7
MASK1
0 = ALERT Enabled
1 = ALERT Masked
6
RUN/STOP 0 = Run
1 = Standby
5–0
Reserved
Power-On
Default
0
0
0
Conversion Rate Register
The lowest three bits of this register are used to program the
conversion rate by dividing the ADC clock by 1, 2, 4, 8, 16, 32,
64, or 128, to give conversion times from 125 ms (Code 07h) to
16 seconds (Code 00h). This register can be written to and read
back over the SMBus. The higher five bits of this register are
unused and must be set to zero. Use of slower conversion times
greatly reduces the device power consumption, as shown in
Table VII.
Table VII. Conversion Rate Register Codes
Data
00h
01h
02h
03h
04h
05h
06h
07h
08h to FFh
Conversion/sec
0.0625
0.125
0.25
0.5
1
2
4
8
Reserved
Average Supply Current
A Typ at VCC = 3.3 V
150
150
150
150
150
150
160
180
Limit Registers
The ADM1023 has six limit registers to store local and remote,
high and low temperature limits. These registers can be written
to and read back, over the SMBus. The high limit registers per-
form a > comparison while the low limit registers perform a
< comparison. For example, if the high limit register is programmed
as a limit of 80°C, measuring 81°C will result in an alarm condi-
tion. Even though the temperature range is 0 to 127°C, it is
possible to program the Limit Register with negative values.
This is for backwards-compatibility with the ADM1021.
One-Shot Register
The one-shot register is used to initiate a single conversion and
comparison cycle when the ADM1023 is in standby mode, after
which the device returns to standby. This is not a data register as
such and it is the write operation that causes the one-shot conver-
sion. The data written to this address is irrelevant and is not stored.
SERIAL BUS INTERFACE
Control of the ADM1023 is carried out via the serial bus. The
ADM1023 is connected to this bus as a slave device, under the
control of a master device.
ADDRESS PINS
In general, every SMBus device has a 7-bit device address (except
for some devices that have extended, 10-bit addresses). When
the master device sends a device address over the bus, the slave
device with that address will respond. The ADM1023 has two
address pins, ADD0 and ADD1, to allow selection of the device
address, so that several ADM1023s can be used on the same bus,
and/or to avoid conflict with other devices. Although only two
address pins are provided, these are three-state, and can be
grounded, left unconnected, or tied to VDD, so that a total of
nine different addresses are possible, as shown in Table VIII.
It should be noted that the state of the address pins is only sampled
at power-up, so changing them after power-up will have no effect.
Table VIII. Device Addresses
ADD0
ADD1
Device Address
0
0
0011 000
0
NC
0011 001
0
1
0011 010
NC
0
0101 001
NC
NC
0101 010
NC
1
0101 011
1
0
1001 100
1
NC
1001 101
1
1
1001 110
ADD0, ADD1 sampled at power-up only.
The serial bus protocol operates as follows:
1. The master initiates data transfer by establishing a START condi-
tion, defined as a high-to-low transition on the serial data line
SDATA, while the serial clock line SCLK remains high. This
indicates that an address/data stream will follow. All slave
peripherals connected to the serial bus respond to the START
condition and shift in the next eight bits, consisting of a 7-bit
address (MSB first) plus an R/W bit, which determines the
direction of the data transfer, i.e., whether data will be written
to or read from the slave device.
The peripheral whose address corresponds to the transmitted
address responds by pulling the data line low during the low
period before the ninth clock pulse, known as the Acknowledge
Bit. All other devices on the bus now remain idle while the
selected device waits for data to be read from or written to it.
If the R/W bit is a 0, the master will write to the slave device. If
the R/W bit is a 1, the master will read from the slave device.
2. Data is sent over the serial bus in sequences of nine clock
pulses, eight bits of data followed by an acknowledge bit
from the slave device. Transitions on the data line must occur
during the low period of the clock signal and remain stable
during the high period, as a low-to-high transition when the
clock is high may be interpreted as a STOP signal. The number
of data bytes that can be transmitted over the serial bus in a
single READ or WRITE operation is limited only by what the
master and slave devices can handle.
3. When all data bytes have been read or written, stop condi-
tions are established. In WRITE mode, the master will pull
the data line high during the 10th clock pulse to assert a STOP
condition. In READ mode, the master device will override
the acknowledge bit by pulling the data line high during the
low period before the ninth clock pulse. This is known as No
Acknowledge. The master will then take the data line low
during the low period before the 10th clock pulse, then high
during the 10th clock pulse to assert a STOP condition.
Any number of bytes of data may be transferred over the serial
bus in one operation, but it is not possible to mix read and write
in one operation, because the type of operation is determined
at the beginning and cannot subsequently be changed without
starting a new operation.
REV. A
–9–
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